Process for making vanillin



Jan. 13, 1948. J. R. sALvEsEN Er Al.

PROCESS FOR MAKING VANILLIN Filed Jan. 22, 1945 jizz/eri fors 1f Richie, SalI/Jew min @3,5m Qms eter OWZdrJ l Patented jan. 13, 1948 PROCESS FOR MAKING VANILLIN Jrgen Richter Salvesen, David L. Brink, and

Donald G. Diddams, Wausau, and Peter Owzarski, Rothschild, Wis., assignors to Salvo Chemical Corporation, Rothschild, Wis., a corporation of Wisconsin Application January zz, 1945, serial 1ra-574,023

(ci. 26o-soo) sciaims. l

This invention relates to a process for making vanillin. More specifically the invention relates to a. process for making vanillin from lignosulfonates by subjecting such products in aqueous solution of caustic alkali to controlled oxidation l by gaseous oxygen or air under elevated temperatures and pressures.

It is known that vanillin can be made by cooking lignosulfonates with aqueous solutions of caustic alkali, but even at optimum conditions as regards lignosulfonate and caustic alkali concentrations, cooking time and temperature, the yield of vanillin is low, whether based on the lignosulfonate or caustic alkali used or in terms of grams per liter of the reaction mixture volume. Manufacturing costs are therefore high. It is further known that the yield of vanillin can be increased by having a selected group of oxidizing agents present during the alkaline cook of lignosulfonates. One type of such oxidizing agents is described in U. S. Patent 2,187,366, January 16, 1930, utilizing aromatic nitro-compounds, and speciiically nitro-benzene. While such process materially increases the vanillin yield, it has the disadvantage that it requires relatively large amounts of the nitro-compounds. This compound is reduced in the process to by-products which cannot be regenerated for re-use, which complicate the subsequent isolation of vanillin and which are diiiicult to dispose of commercially as large amounts are involved.

Gaseous oxygen or `air represent oxidizing agents with none of the disadvantages mentioned above. Kurschner (E. Hagglunds book "Holzchemie i939, p. 165) claimed that by passing oxygen or air through a boiling solution of lignosulfonate and caustic alkali, an improved vanillin yield was found, but this was later denied Holzchemie p. 165-66). In U. S. application Serial No. 318,386, filed February l0, 1940, now abandoned, by Karl Freudenberg et al. (vested in the Alien Property Custodian and published April 20, 1943) vanillin formation from lignin in alkaline solution, heated with oxidizing agents also gaseous oxygen and air-is egaindisclosed. The statement is specifically made in this application that the cooking temperature is a moderate temperature of 100 to 110, in no case more than about 140.

We have tested the various conditions given in the prior art for increasing the vanillin yield from lignosulfonate-caustic alkali cooks employing oxygen or air as oxidizing agents, and have found that the procedures given fail to give desirable results.

We have performed numerous experiments dealing with the various reaction conditions for vanillin formation from lignosulfonates in caustic alkaline solutions with gaseous oxygen and air as oxidizing agents and have discovered methods and conditions for obtaining substantially increased vanillin by practical and economical means, as herewith disclosed.

We have discovered that the most important factors for obtaining optimum vanillin yield are cooking temperature. time and weight of oxygen used in relation to lignosulfonate present. The best yield is thus obtained by employing a cooking temperature around 160 C. with a cooking time of to 110 minutes and by arranging for an oxygen consumption during that cooking time of about 25 to about 35 gms. oxygen per 100 gm. lignin equivalent of the lignosulfonate present in the cooking mixture. Cooking temperatures substantially over 170 C. give erratic results, evidently because over or under oxidation is diiiicult to avoid at the shorter cooking-time required at the higher temperatures. Cooking temperatures substantially below 160 C. are less favorable because maximum yields of vanillin then never are as high as in the examples given later, and cooking time must be extended over several hours which is less desirable from a practical standpoint. For these reasons the practical range of cooking temperature is between 140 and 170 C. and with corresponding cooking time from three hours at the lowest to minutes at the highest cooking temperature. The gaseous oxygen or air should be introduced throughout the entire cooking time, evidently to superimpose the oxidation reaction on the alkaline degradation of the lignosulfonates. If the cook is made without introduction of oxygen or air, then the charge recooked with oxygen or air introduced, the improved vanillin yield is not achieved. The partial pressure of oxygen or air is not critical and a variation from a few pounds partial pressure of oxygen to 40 pounds is used.

We have found that optimum vanillin yield is obtained over the Whole cooking temperature range above specied when 25 to 35 grams O2 is consumed during the cook per grams lignin equivalent of the lignosulfonate present in the cooking mixture.

In our process we prefer to use as starting material a lignosulfonate which is substantially free from non-ligneous organic matter, as the latter would consume oxidizing agent as well as caustic alkali without contributing to the vanillin yield. Thus the basic-calcium lignosulfonate obtained as 3 described in U. S. Patent Re-issue No. 18,268. December 1, 1931, is a. preferred starting material, but other more or less pure lignosulfonates are also applicable to the process provided proper allowances are made for caustic alkali and oxygen consumption of the non-ligneous organic matter that is present in such more crude lignosulfonates.

The lignosulfonate concentration can be varied within fairly wide limits. thus equivalent to from 40 to 200 grams lignin per liter of reaction mixture. and the`corresponding sodium hydroxide concentration is then from 80 to 200 grams per liter.

In order to effect the proper rate of oxygen consumption a suiiicient contact betweenoxygen and liquor is necessary. This may be eiected by spraying oxygen or air into the lignosulfonate containing liquor or by spraying the lignosulfonate containing liquor into an atmosphere of oxygen or air. In the annexed drawing, Figure 1 illustrates a schematic diagram of a type of apparatus for carrying out the present method by which suicient contact between the lignosulfonate containing liquor and oxygen is accomplished. Figure 2 is a fragmental enlarged sectional View of the stirring and oxygen distributing member. The invention, however, is not limited to an apparatus of this type which merely serves as an illustration of one method in practicing the invention.

Referring to the drawing, numeral l is a reaction vessel that is provided with a motor 2 which actuates a stirring and oxygen distributing member 5. The stirring member 5 is provided with an opening I in the vapor space of the reaction vessel l. The center 6 of the stirring device is drilled out from the opening 4 in the vapor space to the end which is in the liquor space. The shaft of the stirring member is provided with blades I6 which have drilled passages i5 that are connected to the drilled passage 8 in the stirring member. As the stirrer is rotated the gases in the `vapor space pass through the opening 4 and the passage 6 in the shaft and are ejected from the passages in the stirring blades by centrifugal action. Oxygen or air is introduced through the inlet tube 1. When air is used the spent air must be removed from the apparatus. Consequently the apparatus is provided with a condenser B. a trap 9, and an air exhaust I0 which permit the removal of spent air without removing any moisture from the reaction vessel. A return line Il connects the trap 9 to the reaction vessel I. When oxygen is used, this system of condenser and trap are not needed and are closed oil? from the rest of the apparatus. A sample line and condenser indicated by numeral at the bottom of diagram are provided in order that liquor samples may be withdrawn from the cooking vessel.

The following examples illustrate conditions that have been used and results that have been obtained in our process:

Example 1.-A liquor containing 231 grams per liter basic-calcium lignosulfonate (corresponding to a lignin content of 150 grams per liter) and 105 grams per liter sodium hydroxide was cooked at 160 C. for 70 minutes in the apparatus described during which time air was introduced into the reaction mixture in suillcient amounts so that 32 grams of oxygen were consumed during the cook for each 100 grams lignin present. The increase in vanillin yield from this cook over that obtained by cooking the same liquor under optimum conditions for maximum vanillin yield without introduction of gaseous oxygen. i. e., minutes at 170 was 82 per cent.

Example 2.-A liquor containing 233 grams per liter basic-calcium lignosulfonate (corresponding to a lignin content of 151 grams per liter) and 108 grams per liter sodium hydroxide was cooked at 170 C. for 90 minutes in the apparatus described during which time oxygen was introduced into the reaction mixture in sufficient amounts s'o that 34 grams of oxygen were consumed during the cook for each grams lignin present. The increase in vanillin yield (see Example 1) was 75 per cent.

Example 3.-A liquor containing 233 grams per liter basic-calcium lignosulfonate (corresponding to a lignin content of 151 grams per liter) and 106 grams per liter sodium hydroxide was cooked at 160 C. for 90 minutes in the apparatus de scribed during which time oxygen was introduced into the reaction mixture in sufficient amounts so that 34 grams of oxygen were consumed during the cook for each 100 grams lignin present. 'I'he increase in vanillin yield (see Example 1) was 81 per cent.

Example 4.A liquor containing 227 grams per liter basic-calcium lignosulfonate (corresponding to a lignin content of 147 grams per liter) and 104 grams per liter sodium hydroxide was cooked at 150 C. for 137 minutes in the apparatus described during which time oxygen was introduced into the reaction mixture insufficient amounts so that 29 grams of oxygen were consumed during the cook for each 100 grams lignin present. The increase in vanillin yield (see Example 1) was 73 per cent.

' Example 5,-A liquor containing 227 grams per liter basic-calcium lignosulfonate (corresponding to a lignin content of 147 grams per liter) and 104 grams per liter sodium hydroxide was cooked at 140 C. for 205 minutes in the apparatus described, during which time oxygen was introduced into the reaction mixture in 'suillcient amounts so that 29 grams of oxygen were consumed during the cook for each 100 grams lignin present. 'I'he increase in vanillin yield (see Example 1) was 69 per cent.

'I'he vanillin formed in our process can be isolated from the cooked liquor by processes known in the art. such as the one described in U. S. Patent No. 2,104,701, January 4, 1938.

It is to be understood that modifications of our process within the ranges of our disclosure are intended to be included within the scope of the appended claims.

We claim:

1. The process of making vanillin which coinprises heating -under autogenic pressure a liquor containing lignosulfonic acid compounds and caustic alkali to a temperature from to 170" C. and continuously introducing oxygen into said liquor until 25 to 35 grams of oxygen per 100 grams of lignin present in the original liquor is consumed.

2. The process of making vanillin which coniprises heating under autogenic pressure a liquor containing lignosulfonic acid compounds and caustic alkali to a temperature above 140 and not over C. and continuously introducing air into said liquor until 25 to 35 grams of oxygen per' 100 grams lignin present in the original liquor is consumed.

3. The process of making vanillin which com prises heating under autogenic pressure a liquor containing lignosulfonic acid compounds and" caustic alkali to a temperature above 140 and not over 170 C. and continuously introducing oxygen into said liquor until 25 to 35 grams of oxygen per 100 grams lignin present in the original liquor is consumed.

4. 'I'he process of making vanillin which comprises heating under autogenic pressure a liquor containing basic calcium lignosulfonic acid compounds and caustic alkali to a temperature above 140 and not over 170 C. and continuously introducing oxygen into said liquor until 25 to 35 grams of oxygen per 100 grams lignin present in the original liquor is consumed.

5. The process of making vanillin which comprises digesting from 60 to 110 minutes under autogenic pressure and liquor containing lignosulionic acid compounds and caustic alkali to a temperature of about 160 C. and continuously introducing oxygen into said liquor until 25 to 35 grams of oxygen per 100 grams lignin present v in the original liquor is consumed.

6. The process of making vanillin which comprises heating under autogenic pressure a. liquor containing lignosulfonic acid compounds and caustic alkali to a temperature of about 160 C. and continuously introducing oxygen into said liquor for about 60 to 110 minutes at such rate that to 35 grams of oxygen are consumed per 100 grams lignin present in the original liquor.

7. The process of making vanillin which comprises heating under autogenic pressure a liquor containing lignosulfonic acid compounds and caustic alkali to a temperature above 140 C. and

not over 170 C., and continuously introducing oxygen into said liquor for about 3 hours at such rate that 25 to 35 grams of oxygen are consumed per 100 grams lignin present in the original liquor.

. 6 8. The process for producing vanillin which comprises preparing an aqueous solution to contain basic-calcium lignosulfonate in the concentration range equivalent to from to 200 grams lignin per liter and a corresponding sodium hydroxide concentration from to 200 grams per liter, cooking said alkali-lignosulfonate solution JRGEN RICHTER sALVEsEN. DAVID L. BRmK.

DONALD G. DIDDAMs.

PETER owzARsKr.

REFERENCES CITED The following references are of record in the flle of this patent:

FOREIGN PATENTSA Number Coimtry Date 67,451 Austria Apr. 1, 1914 513,755 Germany Dec. 14, 1931 Germany Dec. 14, 1931 OTHER REFERENCES Lautsch' et al., Angewandte Chemie, vol. 53, Sept. 28, 1940, pages 450-452. Ser. No. 318,386, Freudenberg (A. P. CJ, pub. Apr. 20, 1943.y 

